1. Field of the Invention
The present invention relates to a receiving circuit and, particularly, to a receiving circuit that receives data on which data matching for equalizing data size of each frame has been performed at the transmitting end.
2. Description of Related Art
A semiconductor device that is mounted on a portable device such as a cellular phone needs to be small so as to achieve a small-size device. In order to achieve a small-size semiconductor device, it is necessary to reduce a circuit scale. In light of this, a technique to reduce the circuit scale of a de-interleaving device that is used in a receiving circuit, which is one of the semiconductor devices to be mounted on a portable device, is disclosed in Japanese Unexamined Patent Application Publication No. 2006-14000.
FIG. 22 shows the configuration of a de-interleaving device 200 described in Japanese Unexamined Patent Application Publication No. 2006-14000. A radio frame buffer 211 is a memory to store a radio frame that is input from the outside (e.g. a de-interleaver that is placed in the previous stage of the de-interleaving device 200 and performs de-interleaving before radio frame combining). The radio frame combiner 212 is a functional section to combine the radio frames stored in the radio frame buffer 211 to form a TTI frame, and it stores the formed TTI frame into a TTI frame buffer 213. Addition of a P-bit is not performed at this time, which is different from a de-interleaving device heretofore used.
A de-interleaver 214 reads the number of P-bits to be inserted into the TTI frame to be de-interleaved from a P-bit information table 215 and further reads a replacement rule from a replacement rule table 216, and then performs bit replacement on each bit of the TTI frame. The TTI frame after replacement is output to the outside of the de-interleaving device 200. Specifically, it is output to a decoding block for decoding the de-interleaved TTI frame.
In the technique disclosed in Japanese Unexamined Patent Application Publication No. 2006-14000, data after radio frame combining is stored in the TTI buffer. After that, de-interleaving is performed by the de-interleaver 214, and then de-rate matching is performed in the subsequent stage. The technique disclosed in Japanese Unexamined Patent Application Publication No. 2006-14000 reduces the capacity of the TTI frame buffer 213 by not adding a P-bit to the TTI frame buffer 213 at this time.
The present inventors, however, have found the following problem. If data is received according to 3GPP specifications, the received data contains data other than data to be decoded because of the rate matching performed at the transmitting end. Thus, de-rate matching, which is the processing reverse to the rate matching performed at the transmitting end, is performed at the receiving end in the 3GPP specifications. The data before the de-rate matching possibly becomes 6.6 times the maximum number of bits (the total of all TrCH) before encoding. It can thus become about 2 times at maximum (in the case of the encoding rate=⅓) the data after encoding, which is before the rate matching. Because the TTI frame buffer of the related art needs to store data before the de-rate matching as described above, it is required to have about two times the capacity of a necessary size as an input of a decoder, causing an increase in circuit scale.